Recently, mobile terminals (such as personal computers, personal digital assistants (PDA), tablet computers) are widespread and high definition of the display images are also progressing. The mobile terminals with highly improved definition each include in its liquid crystal display as a display unit a very much increased number of pixels. The liquid crystal displays are driven with driver IC chips. The driver IC chips are formed from integrated circuits of silicon semiconductor devices, and the integrated circuits include an increasing number of output lines as the definition of the display images is enhanced.
As a result, the high-definition liquid crystal displays consume significantly high power as compared to before. As the power consumption increases, it becomes difficult to drive this liquid crystal display as a mobile terminal by a battery for a long time.
As a concept for reducing the power consumption, there is a method of driving a liquid crystal display at low voltage amplitude. But in order to achieve this method, it is necessary to realize a novel liquid crystal material operable at low voltage amplitude. At present, a novel liquid crystal material operable at low voltage amplitude and also available at low cost has not been developed.
In the meantime, for example, an active-matrix liquid crystal display includes pixel circuits arranged in a matrix. Each pixel circuit comprises a thin film transistor (TFT) which is controlled to be on/off by a gate line. In a write period, the TFT is turned on and an image signal (voltage) is written in between a pixel electrode and a common electrode for driving the liquid crystals. In a display period, the TFT is turned off and the voltage between the pixel electrode and the common electrode is retained, thereby maintaining the drive state of the liquid crystal molecules.
However, when it becomes possible to drive a liquid crystal display with low voltage amplitude as described above, the leak current of the TFT cannot be neglected. If the voltage between a pixel electrode and a common electrode is fluctuated due to leak current, the quality of the image display state by the respective pixel circuit is degraded. Further, if the leak current value varies among pixel circuits, the quality of the image display is also deteriorated.